Representative examples of a related art packet-based transmission technique include Slotted ALOHA and Carrier Sense multiple Access (CSMA) techniques. In the Slotted ALOHA, when a packet to be transmitted is generated in each node under the circumstance where time synchronization between nodes participating in every transmission has been made, the packet is transmitted during the next time slot. Simultaneous transmission made by at least two nodes during a single time slot is called collision, and in the case of collision, packets undergo transmission failure and are re-transmitted after waiting for a random time slot. An ALOHA protocol is significantly simple but an ALOHA-based transmission scheme has lower performance than CSMA and thus is being used in satellite communication for national defense, radio-frequency identification (RFID) and the like using a small bandwidth.
The CSMA technique includes a carrier sensing process in which before transmission, it is checked whether or not someone else is carrying out transmission through a channel. If there is information to be sent, a packet is transmitted when it is determined that no one is using a channel as a result of the carrier sensing. By using this process, the probability of collision, caused by simultaneous transmission by two nodes as in the Slotted ALOHA, may be reduced. Ethernet, constituting a Local Area Network (LAN), adopts CSMA/Collision Detection (CD) additionally equipped with a collision detection function. As for the CSMA/CD, channel sensing is continuously performed even during transmission, and the transmission is stopped when transmission by another node is detected. In a wireless LAN, (WLAN), CSMA/Collision Avoidance (CA) is used to avoid collision. Since transmission and reception cannot be performed at the same time in a radio environment, the CSMA/CD cannot be used, and the CSMA/CA is used in order to address a hidden node problem. In the CSMA/CA, the process of determining which node will perform transmission may be performed by using a Request to Send (RTS) message and a Clear to Send (CTS) message.
The biggest issue of the Slotted ALOHA is the occurrence of collision. The collision degrades the traffic volume of a network.
The problem of the CSMA is that since every node has the same transmission probability value, heavy load on an access point cannot be effectively dealt with.